www.elsevier.com/locate/envint

Environment International 31 (

Review article

Chromium toxicity in plants

Arun K. Shankera,T,1, Carlos Cervantesb, Herminia Loza-Taverac, S. Avudainayagamd

aDepartment of Crop Physiology, Tamil Nadu Agricultural University. Coimbatore, IndiabInstituto de Investigaciones Quımico-Biologicas, Universidad Michoacana, Edificio B-3, Ciudad Universitaria, 58290 Morelia, Michoacan, Mexico

cDepartamento de Bioquımica y Biologıa Molecular de Plantas, Facultad de Quımica, Universidad Nacional Autonoma de Mexico. Mexico, D.F., MexicodDepartment of Environmental Sciences, Tamil Nadu Agricultural University, Coimbatore, India

Received 1 September 2004

Available online 24 March 2005

Abstract

Due to its wide industrial use, chromium is considered a serious environmental pollutant. Contamination of soil and water by chromium

(Cr) is of recent concern. Toxicity of Cr to plants depends on its valence state: Cr(VI) is highly toxic and mobile whereas Cr(III) is less toxic.

Since plants lack a specific transport system for Cr, it is taken up by carriers of essential ions such as sulfate or iron. Toxic effects of Cr on

plant growth and development include alterations in the germination process as well as in the growth of roots, stems and leaves, which may

affect total dry matter production and yield. Cr also causes deleterious effects on plant physiological processes such as photosynthesis, water

relations and mineral nutrition. Metabolic alterations by Cr exposure have also been described in plants either by a direct effect on enzymes

or other metabolites or by its ability to generate reactive oxygen species which may cause oxidative stress. The potential of plants with the

capacity to accumulate or to stabilize Cr compounds for bioremediation of Cr contamination has gained interest in recent years.

D 2005 Elsevier Ltd. All rights reserved.

Keywords: Chromium; Toxicity; Plants; Crops; Cr(III); Cr(VI); Photosynthesis; Phytoremediation; Bioremediation; Uptake; Translocation; Reactive Oxygen

Species; Oxidative stress; Heavy metals

Contents

1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740

2. Chromium in the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740

3. Chromium as an environmental contaminant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740

4. Toxic effects of chromium in plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741

4.1. Chromium uptake, translocation and accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 741

4.2. Growth and development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742

4.2.1. Germination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 742

4.2.2. Root growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743

4.2.3. Stem growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743

4.2.4. Leaf growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743

4.2.5. Total dry matter production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744

4.2.6. Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744

4.3. Physiological processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744

4.3.1. Photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744

0160-4120/$ - see front matter D 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.envint.2005.02.003

T Corresponding author. Tel./fax: +91 517 273064.

E-mail address: arunshanker@mailcan.com (A.K. Shanker).

URL: http://www.geocities.com/arunshank (A.K. Shanker).1 Present address: National Research Centre for Agroforestry, Jhansi, Uttar Pradesh, India.

2005) 739–753

A.K. Shanker et al. / Environment International 31 (2005) 739–753740

4.3.2. Water relations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745

4.3.3. Mineral nutrition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746

4.4. Enzymes and other compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747

4.4.1. Nitrate reductase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747

4.4.2. Root Fe(III) reductase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747

4.4.3. Plasma membrane H+ ATPase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747

4.4.4. Antioxidant enzymes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747

4.4.5. Glutathione . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 748

5. Cr plant tolerance and phytoremediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749

6. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 749

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 750

Table 1

Chromium concentrations in the environment

Sample type Concentration

Natural soils 5–1000 mg kg�1

5–3000 mg kg�1

5–1500 mg kg�1

30–300 mg kg�1

trace to 5.23%

Serpentine soils 634–125,000 mg kg�1

1. Introduction

Chromium (Cr) was first discovered in the Siberian red

lead ore (crocoite) in 1798 by the French chemist Vauquelin.

It is a transition element located in the group VI-B of the

periodic table with a ground-state electronic configuration

of Ar 3d54s1. The stable forms of Cr are the trivalent Cr(III)

and the hexavalent Cr(VI) species, although there are

various other valence states which are unstable and short-

lived in biological systems. Cr(VI) is considered the most

toxic form of Cr, which usually occurs associated with

oxygen as chromate (CrO42�) or dichromate (Cr2O7

2�)

oxyanions. Cr(III) is less mobile, less toxic and is mainly

found bound to organic matter in soil and aquatic environ-

ments (Becquer et al., 2003). Contamination of soil and

ground water due to the use of Cr in various anthropomor-

phic activities has become a serious source of concern to

plant and animal scientists over the past decade.

Cr, in contrast to other toxic trace metals like cadmium,

lead, mercury and aluminum, has received little attention

from plant scientists. Its complex electronic chemistry has

been a major hurdle in unraveling its toxicity mechanism in

plants. The impact of Cr contamination in the physiology of

plants depends on the metal speciation, which is responsible

for its mobilization, subsequent uptake and resultant toxicity

in the plant system. Cr toxicity in plants is observed at

multiple levels, from reduced yield, through effects on leaf

and root growth, to inhibition on enzymatic activities and

mutagenesis.

World soils 200 mg kg�1 (mean)

100–300 mg kg�1

10–150 mg kg�1 (mean 40 mg kg�1)

US soils 25–85 mg kg�1 (mean 37 mg kg�1)

57 mg kg�1 (mean)

Canadian soils 100–5000 mg kg�1 (mean 43 mg kg�1)

Japanese soils 87 mg kg�1 (mean)

Swedish soils 74 mg kg�1 (mean)

Sediments 0–31,000 mg kg�1

Fresh water 0–117 Ag L�1 (average 9.7 Ag L�1)

Sea water 0–0.5 Ag L�1

Air 1–545,000 ng m3

100 ng m3

Plants 0.006–18 mg kg�1

Animals 0.03–1.6 mg kg�1

Modified from Zayed and Terry (2003) with permission.

2. Chromium in the environment

Chromium is found in all phases of the environment,

including air, water and soil (Table 1). Naturally

occurring in soil, Cr ranges from 10 to 50 mgd kg�1

depending on the parental material. In ultramafic soils

(serpentine), it can reach up to 125 gd kg�1 (Adriano,

1986). In fresh water, Cr concentrations generally range

from 0.1 to 117 Ag L�1, whereas values for seawater

range from 0.2 to 50 Ag L�1. Cr concentration varies

widely in the atmosphere, from background concentra-

tions of 5.0�10�6–1.2�10�3 Agdm�3 in air samples

from remote areas such as Antarctica and Greenland to

0.015–0.03 Agd m�3 in air samples collected over urban

areas (Nriagu, 1988). Cr(VI) is a strong oxidant with a

high redox potential in the range of 1.33–1.38 eV

accounting for a rapid and high generation of ROS and

its resultant toxicity (Shanker et al., 2004a,b, in press).

3. Chromium as an environmental contaminant

Cr and its compounds have multifarious industrial uses.

They are extensively employed in leather processing and

finishing (Nriagu, 1988), in the production of refractory

steel, drilling muds, electroplating cleaning agents, catalytic

manufacture and in the production of chromic acid and

specialty chemicals. Hexavalent chromium compounds are

used in industry for metal plating, cooling tower water

treatment, hide tanning and, until recently, wood preserva-

tion. These anthropogenic activities have led to the wide-

spread contamination that Cr shows in the environment and

A.K. Shanker et al. / Environment International 31 (2005) 739–753 741

have increased its bioavailability and biomobility. A

detailed review on the critical assessment of Cr in the

environment has been published by Kimbrough et al.

(1999), Kotas and Stasicka (2000).

The leather industry is the major cause for the high influx

of Cr to the biosphere, accounting for 40% of the total

industrial use (Barnhart, 1997). In India, about 2000–32,000

tons of elemental Cr annually escape into the environment

from tanning industries. Even if the recommended limit for

Cr concentration in water are set differently for Cr(III) (8 AgL�1) and Cr(VI) (1 Ag L�1), it ranges from 2 to 5 g/L in the

effluents of these industries (Chandra et al., 1997). In the

United States, 14.6 Ag L�1 in ground water and 25.9 gd kg�1

in soil have been found in the vicinity of chrome production

sites (Zayed and Terry, 2003).

4. Toxic effects of chromium in plants

Chromium compounds are highly toxic to plants and are

detrimental to their growth and development. Although

some crops are not affected by low Cr concentration

(3.8�10�4 AM) (Huffman and Allaway, 1973a,b), Cr is

toxic to most higher plants at 100 AMd kg�1 dry weight

(Davies et al., 2002). In the following sections, we review

several of the metabolic and physiological processes

affected by Cr in plants.

4.1. Chromium uptake, translocation and accumulation

The first interaction Cr has with a plant is during its

uptake process. Cr is a toxic, nonessential element to plants;

hence, they do not possess specific mechanisms for its

uptake. Therefore, the uptake of this heavy metal is through

carriers used for the uptake of essential metals for plant

metabolism. The toxic effects of Cr are primarily dependent

Apoplast

Transport protein

Medium/ Rhizoplane

Cr(III) Cr(III)

Cr(III)

Cr(III) Cr(VI)

Cr(VI)SO4(II)/Fe(III)

Cr(VI)PM ATPase

Oxidation ?

C

Cr

Pla

Cytopl

Defense/To

Cr(

Fig. 1. Hypothetical model of chromium transport and to

on the metal speciation, which determines its uptake,

translocation and accumulation (Fig. 1). The pathway of

Cr(VI) transport is an active mechanism involving carriers

of essential anions such as sulfate (Cervantes et al., 2001).

Fe, S and P are known also to compete with Cr for carrier

binding (Wallace et al., 1976).

Uptake and accumulation of Cr by various crops are well

documented (Table 2). Independent uptake mechanisms for

Cr(VI) and Cr(III) have been reported in barley. The use of

metabolic inhibitors diminished Cr(VI) uptake whereas it

did not affect Cr(III) uptake, indicating that Cr(VI) uptake

depends on metabolic energy and Cr(III) does not (Skef-

fington et al., 1976). In contrast, an active uptake of both Cr

species, slightly higher for Cr(III) than for Cr(VI), was

found in the same crop (Ramachandran et al., 1980).

In 7 out of 10 crops analyzed, more Cr accumulated

when plants were grown with Cr(VI) than with Cr(III)

(Zayed et al., 1998). Skeffington et al. (1976) from

radioactive tracer studies using 51Cr reported that Cr mainly

moved in the xylem of the plants. Golovatyj et al. (1999)

have shown that Cr distribution in crops had a stable

character which did not depend on soil properties and

concentration of this element; the maximum quantity of

element contaminant was always contained in roots and a

minimum in the vegetative and reproductive organs. In

bean, only 0.1% of the Cr accumulated was found in the

seeds as against 98% in the roots (Huffman and Allaway,

1973a). The reason of the high accumulation in roots of the

plants could be because Cr is immobilized in the vacuoles of

the root cells, thus rendering it less toxic, which may be a

natural toxicity response of the plant (Shanker et al., 2004a).

Since both Cr(VI) and Cr(III) must cross the endodermis via

symplast, the Cr(VI) in cells is probably readily reduced to

Cr(III) which is retained in the root cortex cells under low

concentration of Cr(VI) which in part explains the lower

toxicity of Cr(III) (Fig. 1). Although higher vascular plants

Vacuole

r(VI)

(VI)

Red

uct

ion

sma Membrane

Cr(VI)

Reduction ?

asm

lerance

SOD

Nucleus

Singlet Oxygen

Cr(VI)Cr(III)

III)

xicity in plant roots. Details are given in the text.

Table 2

Relationship between chromium concentration in growth medium and its uptake in crops

Cr concentration in medium Uptake and accumulation pattern Crop/plant Reference

0, 5, 30, 45, 60, 75, 90, 105, 120 and

135 mg kg�1 Cr(III) and Cr(VI)

2.8 Cr(III) and 3.14 Cr(VI) Ag g�1 Spinach Singh (2001)

0, 5, 10, 20 and 40 ppm Cr(IV) Progressive increase with more

Cr in roots than shoots

Lucerne Peralta et al. (2001)

Total Cr 1 ppm 10–200 times in roots Veronica beccabanga and

several hydrophytes

Zurayk et al. (2001)

0, 100, 300, 500,

1000 mg kg�1 Cr(III)

Mobile soil Cr�Plant Cr (r=0.965) Medicago sativa Zlatareva et al. (1999)

Total soil Cr�Plant Cr (r=0.629)

50, 100, 200 AM Cr(VI) Progressive increase with more Cr in

roots than shoots

Nelumbo nucifera Vajpayee et al. (1999)

6, 12, 24 mg L�1 Cr Cr more in roots than shoots in A and

more in shoots than roots in B

A: Dactylis glomerate Shanker (2003)

B: Medicago sativa

1 mg L�1 for 10 days Cr Shoot: 44 mg kg�1 DW Smart weed Jin-Hong et al. (1999)

Root: 2980 mg kg�1 DW

0.5,1,5, 25 Ag mL�1 51Cr

radio-labelled

Progressive increase with more Cr

in roots than shoots

Rice Mishra et al. (1997)

0, 50, 100 mg L�1 Cr(III) roots took up more than shoots and

not detected in fruits

Tomato Moral et al. (1996)

0–200 mg kg �1 Progressive increase with more Cr in

roots than shoots

Sunflower, maize and

Vicia faba

Kocik and Ilavsky (1994)

0.25 and 1.0 mg L�1 L 75–100% steady state removal; 1–2 mg kg�1

DW at the rate of 250–667 mg day�1 m2

Lemna minor Wahaab et al. (1995)

Tannery effluent Progressive increase with more Cr in roots

than shoots, 38 ppm accumulation

Eichornia crassipes Singaram (1994)

Tannery effluent 38–50% removal of Cr Hydrilla verticiliata Vajpayee et al. (1995)

10 ppm r 105–156 Ag g�1 accumulation Eichornia crassipes Saltabas and Akcin (1994)

0, 5, 50, 150 and 300 Ag mL�1 Cr(III)

and Cr(VI)

70–90% accumulation in roots Allium cepa Srivastava et al. (1994)

Tannery effluent 5%, 10% and 15% High Cr removal from 10% and 15% Swiss Chard Grubinger et al. (1994)

0, 2, 4, 6, 8 mg L�1 6700 mg kg�1 in roots Veronica beccabanga Zurayk et al. (2001)

0, 100, 500 Cr(VI) and Cr(VI) 2.4 mg kg�1 shoot and 115.6

mg kg�1 in root in A

A: sorghum Shahandeh and Hossner,

2000a

5.8 mg kg�1 shoot and 212 mg kg�1

in root in B

B: sunflower

19.2 AM Cr(VI) and 19.2 AM Cr( III) 350 mg kg�1 roots and 2 mg kg�1

shoots

Cauliflower, kale,

and cabbage

Zayed et al. (1998)

0, 0.05, 0.10, 0.50, 1.00 and 5.00 ppm 11.9–32.8 ppm in tops Soybean Turner and Rust (1971)

0. 0.2, 2 and 10 ppm total Cr Progressive increase with increase

in C concentration

Cabbage Hara and Sonoda (1979)

A.K. Shanker et al. / Environment International 31 (2005) 739–753742

do not contain Cr(VI)-reducing enzymes, they have been

widely reported in bacteria and fungi (Cervantes et al.,

2001).

4.2. Growth and development

Plant growth and development are essential processes of

life and propagation of the species. They are continuous and

mainly depend on external resources present in soil and air.

Growth is chiefly expressed as a function of genotype and

environment, which consists of external growth factors and

internal growth factors. Presence of Cr in the external

environment leads to changes in the growth and develop-

ment pattern of the plant. These effects are summarized in

Table 3.

4.2.1. Germination

Since seed germination is the first physiological process

affected by Cr, the ability of a seed to germinate in a

medium containing Cr would be indicative of its level of

tolerance to this metal (Peralta et al., 2001). Seed

germination of the weed Echinochloa colona was reduced

to 25% with 200 AM Cr (Rout et al., 2000). High levels (500

ppm) of hexavalent Cr in soil reduced germination up to

48% in the bush bean Phaseolus vulgaris (Parr and Taylor,

1982). Peralta et al. (2001) found that 40 ppm of Cr(VI)

reduced by 23% the ability of seeds of lucerne (Medicago

sativa cv. Malone) to germinate and grow in the contami-

nated medium. Reductions of 32–57% in sugarcane bud

germination were observed with 20 and 80 ppm Cr,

respectively (Jain et al., 2000).

The reduced germination of seeds under Cr stress

could be a depressive effect of Cr on the activity of

amylases and on the subsequent transport of sugars to the

embryo axes (Zeid, 2001). Protease activity, on the other

hand, increases with the Cr treatment, which could also

contribute to the reduction in germination of Cr-treated

seeds (Zeid, 2001).

Table 3

Effects of chromium on plant growth and development

Process Crop/plant Effects References

Germination E. colona, bush bean, lucerne,

mung bean, sugarcane

Reduced germination percentage and

reduced bud sprouting

Rout et al. (2000), Peralta et al.

(2001), Parr and Taylor (1982), Jain

et al. (2000), Corradi et al. (1993)

Root growth Salix viminalis, Caesalpinia

pulcherrima, mung bean,

rice, sorghum

Decrease in root length and dry

weight, increase in root diameter and

root hairs, proportional variations in

cortical and pith tissue layers

Prasad et al. (2001), Iqbal et al.

(2001), Panda and Patra (2000),

Suseela et al. (2002) Shanker (2003)

Shoot growth Oats, Curcuma sativa, Lactuca

sativa,

Panicum miliaceum, Sinapsis alba

Reduction in plant height Anderson et al. (1972), Joseph et al.

(1995), Barton et al. (2000), Sharma

and Sharma (1993), Hanus and

Tomas (1993), Mei et al. (2002)

Leaf growth Albizia lebbek, Acacia holocerica,

Leucaena luecocephala,

rice, bush bean

Reduction in leaf number leaf area

and biomass. Trifoliate leaves more

affected than primary leaf in legumes;

scorching of leaf tip, negative effect

on leaf mesostructure

Sharma and Sharma (1993), Tripathi

et al. (1999), Barcelo et al. (1985),

Karunyal et al. (1994), Pochenrieder

et al. (1993), Shanker (2003)

Yield and dry

matter production

Portaluca oleracea, cauliflower,

cabbage, radish, bush bean,

maize, finger millet, faba beans

up to 50% reduction in yield, reduced

number of flowers per plant, reduced

grain weight, increased seed

deformity, reduced pod weight

Vajpayee et al. (2001), Zurayk et al.

(2001), Chatterjee and Chatterjee,

2000, Biacs et al. (1995), Jetly and

Srivastava (1995), McGrath (1982)

A.K. Shanker et al. / Environment International 31 (2005) 739–753 743

4.2.2. Root growth

Decrease in root growth is a well-documented effect due

to heavy metals in trees and crops (Breckle, 1991; Goldbold

and Kettner, 1991; Tang et al., 2001) (Table 3). Prasad et al.

(2001) reported that the order of metal toxicity to new root

primordia in Salix viminalis is CdNCrNPb, whereas root

length was more affected by Cr than by other heavy metals

studied. Root length and dry weight of the important arid

tree Caesalpinia pulcherrima was inhibited by 100 ppm Cr

(Iqbal et al., 2001). Total root weight and root length of

wheat was affected by 20 mg Cr(VI) kg�1 soil as K2Cr2O7

(Chen et al., 2001). Panda and Patra (2000) found that 1 AMof Cr increased the root length in seedlings growing under

nitrogen (N) nutrition levels; higher Cr concentrations

decreased root length in all the N treatments. Samantaray

et al. (1999), in a study with chromite mine spoil soil in five

cultivars of mung bean, noted that root growth was

significantly affected 28 days after root emergence.

Scanning electron microscope studies of roots affected

by Cr showed increased growth of root hairs and increased

relative proportion of pith and cortical tissue layers (Suseela

et al., 2002). General response of decreased root growth due

to Cr toxicity could be due to inhibition of root cell division/

root elongation or to the extension of cell cycle in the roots.

Under high concentrations of both the Cr species combina-

tion, the reduction in root growth could be due to the direct

contact of seedlings roots with Cr in the medium causing a

collapse and subsequent inability of the roots to absorb

water from the medium (Barcelo et al., 1986).

4.2.3. Stem growth

Adverse effects of Cr on plant height and shoot growth

have been reported (Rout et al., 1997). When Cr was added

at 2, 10 and 25 ppm to nutrient solutions in sand cultures in

oats, Anderson et al. (1972) observed 11%, 22% and 41%

reduction in plant height, respectively, over control.

Reduction in plant height due to Cr(VI) on Curcumas

sativus, Lactuca sativa and Panicum miliaceum was

reported by Joseph et al. (1995). Barton et al. (2000)

observed that Cr(III) addition inhibited shoot growth in

lucerne cultures. Sharma and Sharma (1993) reported that

after 32 and 96 days, plant height reduced significantly in

wheat cv. UP 2003 in a glasshouse trial when sown in sand

with 0.5 AM sodium dichromate. There was a significant

reduction in plant height in Sinapsis alba when Cr was

given at the rates of 200 or 400 mg kg�1 soil along with N,

P, K and S fertilizers (Hanus and Tomas, 1993). The

reduction in plant height might be mainly due to the reduced

root growth and consequent lesser nutrients and water

transport to the above parts of the plant. In addition to this,

Cr transport to the aerial part of the plant can have a direct

impact on cellular metabolism of shoots contributing to the

reduction in plant height.

4.2.4. Leaf growth

Leaf growth, area development and total leaf number

decisively determine the yield of crops (Table 3). Leaf

number per plant reduced by 50% in wheat when 0.5 mM

Cr was added in nutrient solution (Sharma and Sharma,

1993). Tripathi et al. (1999) found that leaf area and biomass

of Albizia lebbek seedlings was severely affected by a high

concentration (200 ppm) of Cr(VI). These authors noted that

leaf growth traits might serve as suitable bioindicators of

heavy metal pollution and in the selection of resistant

species. Primary and trifoliate leaves of bush bean plants

grown in 1–10 Ag cm�3 Cr showed a marked decrease in

leaf area; trifoliate leaves were more affected by Cr than the

primary leaves (Barcelo et al., 1985). Dry leaf yield of bush

A.K. Shanker et al. / Environment International 31 (2005) 739–753744

bean plants was found to decrease up to 45% when 100 ppm

of Cr(VI) was added to soil (Wallace et al., 1976). Karunyal

et al. (1994) studied the effect of tannery effluent on leaf

area and biomass and reported that all the concentrations

tested decreased leaf area and leaf dry weight in Oryza

sativa, Acacia holosericea and Leucaena leucocephala.

In a study on the effect of Cr(III) and Cr(VI) on spinach,

Singh (2001) reported that Cr applied at 60 mg kg�1 and

higher levels reduced the leaf size, caused burning of leaf

tips or margin and slowed leaf growth rate. Jain et al. (2000)

observed leaf chlorosis at 40 ppm Cr that turned to necrosis

at 80 ppm Cr. In a study with several heavy metals, Pedreno

et al. (1997) found that Cr had a pronounced effect on leaf

growth and preferentially affected young leaves in tomato

plants. Reduction in leaf biomass was correlated with the

oxalate acid extractable Cr in P. vulgaris by Poschenrieder

et al. (1993).

4.2.5. Total dry matter production

The first prerequisite for higher yields in plants is an

increase in biomass production in terms of dry matter.

Carbon compounds account for 80–90% of the total dry

matter produced by plants. Higher source size and increased

photosynthetic process was found to be the basis for the

building up of organic substances and dry matter production

under heavy-metal stress in general and Cr in particular

(Bishnoi et al., 1993a,b) (Table 3).

In a study conducted on Vallisneria spiralis to evaluate

the Cr accumulation and toxicity in relation to biomass

production, it was found that dry matter production was

severely affected by Cr(VI) concentrations above 2.5 AgmL�1 in nutrient medium (Vajpayee et al., 2001). Zurayk et

al. (2001) reported that salinity and Cr(VI) interaction

caused a significant decrease in the dry biomass accumu-

lation of Portulaca oleracea. Cauliflower (cv. Maghi) when

cultivated at 0.5 mM Cr(VI) restricted dry biomass

(Chatterjee and Chatterjee, 2000). Kocik and Ilavsky

(1994) studied the effect of Cr on quality and quantity of

biomass in sunflower, maize and Vicia faba and observed

that dry matter production was not markedly affected by 200

mg kg�1 Cr(VI), but uptake of Cr into plant tissue was

positively correlated with their contents in the soil. There

was a distinct reduction in dry biomass at flowering stage in

S. alba when Cr(VI) was given at the rates of 200 or 400 mg

kg�1 soil along with N, P, K and S fertilizers (Hanus and

Tomas, 1993). P. vulgaris and maize plants exposed to 1 AMCr(III) showed higher root and leaf dry weight (DW) than

controls, and this increase in DW was more pronounced in

Fe-deficient conditions (Barcelo et al., 1993). Cabbage

plants water cultured under Cr exhibited a marked reduction

in dry weight of whole plant from 88.4 g plant�1 in control

to 28.4 g plant�1 in 10 ppm Cr (Hara and Sonoda, 1979).

4.2.6. Yield

Most physiological and biochemical processes are

severely affected by Cr, and as a consequence, the yield

and productivity of the crops are equally affected (Barcelo et

al., 1993) (Table 3). In pot trials with soil amendment of Cr

at the levels of 100 or 300 mg kg�1, Golovatyj et al. (1999)

reported reduction in yield of barley and maize. No

harvestable yield was obtained where Cr was applied at

270 or 810 kg ha�1 in carrot (Biacs et al., 1995). In wheat

the number of flowers per plant decreased by N50% at 0.05

AM Cr compared with the control and even more with 0.5

AM Cr. The number of grains per plant decreased 59% from

the control in 0.05 AM Cr. Grain DW was highest in the

control and was reduced by 58–92% with increase in Cr

level. Tillering was reduced and seed deformities increased

with increase in Cr level (Sharma and Sharma, 1993).

Sharma and Mehrotra (1993) found that seed DW yield was

2.11 g per plant without Cr, and 0.39 g and 0.16 g with 20

and 200 ppm of Cr, respectively. The effect of Cr on the

plant processes during early growth and development

culminates in reduction of yield and total dry matter as a

consequence of poor production, translocation and parti-

tioning of assimilates to the economic parts of the plant. The

negative effect on yield and dry matter is essentially an

indirect effect of Cr on plants. The overall adverse effect of

Cr on growth and development of plants could be serious

impairment of uptake of mineral nutrients and water leading

to deficiency in the shoot. In addition, the normal

mechanism of selective inorganic nutrient uptake may have

been destroyed by oxidative damage, thus permitting larger

quantities of Cr(VI) to enter the roots passively and further

translocation of Cr(VI) to shoot causing oxidative damage to

the photosynthetic and mitochondrial apparatus eventually

reflecting in poor growth. In contrast, Cr(III) is kinetically

inert to ligand substitution and therefore can form sub-

stitution inert metaloprotein complexes in vivo, thus greatly

reducing its role in causing toxic symptoms. The toxicity of

Cr(III) is reported to be due to indirect effects such as

changes in pH and/or inhibition of ion transport.

4.3. Physiological processes

These toxic effects are summarized in Table 4.

4.3.1. Photosynthesis

Chromium stress is one of the important factors that

affect photosynthesis in terms of CO2 fixation, electron

transport, photophosphorylation and enzyme activities

(Clijsters and Van Assche, 1985) (Table 4). In higher plants

and trees, the effect of Cr on photosynthesis is well

documented (Foy et al., 1978; Van Assche and Clijsters,

1983). However, it is not well understood to what extent Cr-

induced inhibition of photosynthesis is due to disorganiza-

tion of chloroplasts ultrastructure (Vazques et al., 1987),

inhibition of electron transport or the influence of Cr on the

enzymes of the Calvin cycle. Chromate is used as a Hill

reagent by isolated chloroplast (Desmet et al., 1975). The

more pronounced effect of Cr(VI) on PS I than on PS II

activity in isolated chloroplasts has been reported by Bishnoi

Table 4

Effects of chromium on plant physiology

Process Crop/plant Effects References

Photosynthesis Wheat, peas, rice, maize,

beans, sunflower

Electron transport inhibition,

Calvin cycle enzyme inactivation,

reduced CO2 fixation, chloroplast

disorganization

Davies et al. (2002),

Bishnoi et al. (1993a,b),

Zeid (2001), Shanker (2003)

Water relations Bush beans, sunflower,

mung bean

Decreased water potential, increased

transpiration rate, reduced diffusive

resistance, wilting, reduction in

tracheary vessel diameter

Vazques et al. (1987),

Barcelo et al. (1986),

Davies et al. (2002)

Mineral nutrition Soybean, tomato, bush bean,

sunflower, maize

Uptake of N, P, K, Fe, Mg, Mn, Mo,

Zn, Cu, Ca, B affected

Moral et al. (1995, 1996),

Khan et al. (2000)

Enzymes and other

compounds

Nymphaea alba and various

cereals and legumes

Inhibition of assimilatory enzymes,

increase activity of ROS scavenging

enzymes, changes in glutathione

pool, no production of phytochelatins

Vajpayee et al. (2000), Panda and

Patra (2000), Barton et al. (2000),

Pillay (1994), Samantaray, 2002,

Shanker (2003), Jain et al. (2000),

Toppi et al. (2002), Bassi et al.

(1990), Behra et al. (1999)

A.K. Shanker et al. / Environment International 31 (2005) 739–753 745

et al. (1993a,b) in peas. Nevertheless, in whole plants, both

the photosystems were affected. Zeid (2001) observed in

peas that Cr at the highest concentration tested (10�2 M)

decreased photosynthesis drastically. Krupa and Baszynski

(1995) explained some hypotheses concerning the possible

mechanisms of heavy-metals toxicity on photosynthesis and

presented a list of key enzymes of photosynthetic carbon

reduction, which were inhibited in heavy-metal treated

plants (mainly cereal and legume crops).

It has been noticed that the 40% inhibition of whole plant

photosynthesis in 52-day-old plants at 0.1 mM Cr(VI) was

further enhanced to 65% and 95% after 76 and 89 days of

growth, respectively (Bishnoi et al., 1993a). Disorganization

of the chloroplast ultrastructure and inhibition of electron

transport processes due to Cr and a diversion of electrons

from the electron-donating side of PS I to Cr(VI) is a

possible explanation for Cr-induced decrease in photo-

synthetic rate. It is possible that electrons produced by the

photochemical process were not necessarily used for carbon

fixation as evidenced by low photosynthetic rate of the Cr-

stressed plants. Due to the known oxidative potential of

Cr(VI), it is possible that alternative sinks for electrons

could have been enhanced by reduction of molecular

oxygen (part of Mehler reaction) which in part explains

the oxidative stress brought about by Cr(VI). The overall

effect of Cr ions on photosynthesis and excitation energy

transfer could also be due to Cr(VI)-induced abnormalities

in the chloroplast ultrastructure like a poorly developed

lamellar system with widely spaced thylakoid and fewer

grana (Van Assche and Clijsters, 1983).

Bioaccumulation of Cr and its toxicity to photosynthetic

pigments in various crops and trees is well documented

(Barcelo et al., 1986; Sharma and Sharma, 1996; Vajpayee

et al., 1999) (Table 4). Bera et al. (1999) studied the effect of

Cr present in tannery effluent on chloroplast pigment

content in mung bean and reported that irrespective of

concentration, chlorophyll a, chlorophyll b and total

chlorophyll decreased in 6-day-old mung bean seedlings

as compared to control. Chlorophyll content was high in

tolerant calluses in terms of survival under high Cr

concentration in a study of Cr and Ni tolerance in E. colona

(Samantaray et al., 2001). Chlorophyll content decreased as

a marked effect of various concentrations of different Cr

compounds [Cr(III) and Cr(VI)] in Triticum aestivum

(Sharma and Sharma, 1996). Cauliflower (cv. Maghi) grown

in refined sand with complete nutrition (control) and at 0.5

mM each of Co, Cr and Cu showed drastic decrease in

chlorophylls a and b in leaves in the order CoNCuNCr

(Chatterjee and Chatterjee, 2000). The influence of 1 and 2

mg L�1 Cr(VI) on Salvinia minima decreased chlorophylls

a and b and carotenoid concentrations significantly (Nichols

et al., 2000). The decrease in the chlorophyll a/b ratio

(Shanker, 2003) brought about by Cr indicates that Cr

toxicity possibly reduces size of the peripheral part of the

antenna complex. The decrease in chlorophyll b due to Cr

could be due to the destabilization and degradation of the

proteins of the peripheral part. The inactivation of enzymes

involved in the chlorophyll biosynthetic pathway could also

contribute to the general reduction in chlorophyll content in

most plants under Cr stress.

4.3.2. Water relations

Wilting of various crops and plant species due to Cr

toxicity has been reported (Turner and Rust, 1971), but little

information is available on the exact effect of Cr on water

relations of higher plants (Table 4). Barcelo et al. (1985)

observed a decrease in leaf water potential in Cr treated bean

plants. Excess Cr decreased the water potential and

transpiration rates and increased diffusive resistance and

relative water content in leaves of cauliflower (Chatterjee

and Chatterjee, 2000). Decreased turgor and plasmolysis

was observed in epidermal and cortical cells of bush bean

plants exposed to Cr (Vazques et al., 1987). Toxic levels of

Cr in beans were found to decrease tracheary vessel

diameter, thereby reducing longitudinal water movement

(Vazques et al., 1987). Impaired spatial distribution and

A.K. Shanker et al. / Environment International 31 (2005) 739–753746

reduced root surface of Cr-stressed plants can lower the

capacity of plants to explore the soil surface for water. The

significantly higher toxic effect of Cr(VI) in declining the

stomatal conductance could be due to the high oxidative

potential of Cr(VI), which in turn may be instrumental in

damaging the cells and membrane of stomatal guard cells.

4.3.3. Mineral nutrition

Chromium, due to its structural similarity with some

essential elements, can affect mineral nutrition of plants in a

complex way. Interactions of Cr with uptake and accumu-

lation of other inorganic nutrients have received maximum

attention by researchers. Cr(III) and Cr(VI) are taken up by

the plants by different mechanisms (Zaccheo et al., 1985). It

has been suggested that both species can interfere with

uptake of several other ionically similar elements like Fe

and S (Skeffington et al., 1976). Nutrient solution with 9.6

AM Cr(VI) decreased the uptake of K, Mg, P, Fe and Mn in

roots of soybean (Turner and Rust, 1971). Excess Cr

interfered with the uptake of Fe, Mo, P and N (Adriano,

1986). Barcelo et al. (1985) described the inhibition of P, K,

Zn, Cu and Fe translocation within the plant parts when

bean plants were exposed to Cr in nutrient solutions. Sujatha

et al. (1996) reported that tannery effluent irrigation caused

micronutrient deficiencies in several agricultural crops.

In soil grown rye grass, the influence of Cr on mineral

nutrition was highly variable and depended on the source of

Cr and soil properties (Ottabbong, 1989a); it was further

found that differences in soluble Mn fractions, interactions

with P and critical effects on the uptake of Mn, Cu, Zn, Fe

and Al were influenced by Cr in rye grass (Ottabbong,

1989b). Cr-induced chlorosis was also observed, whereas

there was no clear correlation between leaf Fe levels and

chlorosis (Ottabbong, 1989c). Cr(VI)-induced decrease in

Ca, K, Mg, P, B and Cu concentrations in soil-grown

soybean tops was observed, but Fe, Mn and Zn uptake was

not affected (Turner and Rust, 1971). In non-calcareous

soils amended with Cr(III), the translocation of Fe, Zn and

Mo to bean plants was decreased (Wallace et al., 1976). In

contrast, other workers supplied Cr in the form of Cr(VI),

Cr(III) or in the form of tannery waste to soils and found an

enhancement of Fe availability and uptake by plants (Cary

et al., 1977a,b; Barcelo et al., 1993).

Barcelo et al. (1985) found high correlation between

chlorophyll pigments and Fe and Zn uptake in Cr-stressed

plants. Moral et al. (1995) reported that the nutrient

elements N, P, K, Na, Ca and Mg concentrations in stems

and branches were significantly affected by the Cr treat-

ments (50 and 100 mg L�1) in tomato. Later, Moral et al.

(1996) conducted a detailed study on the mineral nutrition

of tomatoes under Cr stress and noted that Cr had a negative

effect on Fe absorption. Competitive interaction between Cr

and Cu in the roots, stems and leaves was confirmed. Mn

was not clearly affected; B and Cr had synergistic

interactions in roots, but an antagonistic effect in the stems

and leaves. In the fruits, Cr treatment had no effect on Fe,

Mn, Cu and Zn contents. B increased with Cr concentration

in the nutrient solution.

In maize (cv. Ganga 5), the effects of Cr on Fe

concentration varied with plant organ and Cr level. Mn

and Cu concentrations generally decreased with increasing

Cr level, while Zn concentration decreased in leaves and

flowers but increased in stem and roots (Sharma and Pant,

1994). In a study on Cr(III)–Fe interaction, Bonet et al.

(1991) reported that Cr enhanced growth of both Fe-control

and Fe-deficient plants. However, Cr concentration was

correlated neither to changes of Mn, P or Fe tissue

concentration nor to Cr-induced alterations of the Fe/Mn

and P/Fe ratios. The reduction in the uptake of the elements

S and Fe could be mainly due to the chemical similarity of

these ions in solution. Dual uptake mechanisms have been

reported for S, P and K (Shewry and Peterson, 1974).

Hence, the competitive binding to common carriers by

Cr(VI) could have reduced the uptake of many nutrients.

One of the reasons for the decreased uptake of most of the

nutrients in Cr-stressed plants could have been because of

the inhibition of the activity of plasma membrane H+

ATPase (Shanker, 2003) (see below). Cr treatment also

markedly inhibited the incorporation of P, K, Ca, Mg, Fe,

Mn, Zn and Cu in different cellular constituents in 1-year-

old West Coast Tall coconut plants growing in pots

(Biddappa and Bopaiah, 1989).

The reduction in N, K, P and other elements could be

due to the reduced root growth and impaired penetration

of the roots into the soil due to Cr toxicity. Khan et al.

(2001) observed that threshold values of the concen-

trations of N, P and K in dry weight of rice plants

showed significant decrease at 0.5 ppm Cr. Excess of Cr

(0.5 mM) caused a decrease in the concentration of Fe

and affected the translocation of P, S, Mn, Zn and Cu

from roots to tops (Chatterjee and Chatterjee, 2000) in

cauliflower. Total P in sunflower hull was highest with

Cr (0.5 ppm) 30 days after flowering (Gupta et al.,

2000), whereas Sharma and Sharma (1996) reported that

leaf P concentration decreased with 0.25 mM Cr in wheat

cv. UP2003. Cr(VI) is actively taken up and is a

metabolically driven processes in contrast to Cr(III)

which is passively taken up and retained by cation-

exchange sites of the cell wall (Shanker et al., 2004a,in

press). This in part explains the higher accumulation of

Cr(VI) by the plants. In addition, it is known that P and

Cr are competitive for surface sites and Fe, S and Mn are

also known to compete with Cr for transport binding .

Hence, it is possible that Cr effectively competed with

these elements to gain rapid entry into the plant system.

Poor translocation of Cr to the shoots could be due to

sequestration of most of the Cr in the vacuoles of the

root cells to render it non-toxic which may be a natural

toxicity response of the plant. It must be noted that Cr is

a toxic and nonessential element to plants, and hence, the

plants may not possess any specific mechanism of

transport of Cr.

A.K. Shanker et al. / Environment International 31 (2005) 739–753 747

4.4. Enzymes and other compounds

Chromium stress can induce three possible types of

metabolic modification in plants (Table 4): (i) alteration in

the production of pigments which are involved in the life

sustenance of plants (e.g., chlorophyll, anthocyanin) (Boo-

nyapookana et al., 2002); (ii) increased production of

metabolites (e.g., glutathione, ascorbic acid) as a direct

response to Cr stress which may cause damage to the plants

(Shanker, 2003); and (iii) alterations in the metabolic pool to

channelise the production of new biochemically related

metabolites which may confer resistance or tolerance to Cr

stress (e.g., phytochelatins, histidine) (Schmfger, 2001).

4.4.1. Nitrate reductase

Nitrate reductase (NR) activity of leaves was signifi-

cantly increased over control values and negatively corre-

lated with root and shoot length, leaf area and biomass of

the plants, indicating stress due to Cr(VI) in A. lebbek

(Tripathi et al., 1999). Cr concentrations up to 200 AMresulted in significant inhibition of NR activity in Nelumbo

nucifera (Vajpayee et al., 1999) and Nymphaea alba

(Vajpayee et al., 2000). Seedlings treated with 1 AM Cr

resulted in increased NR activity, whereas higher Cr

concentrations were toxic and reduced the enzyme activity

significantly in wheat (Panda and Patra, 2000).

4.4.2. Root Fe(III) reductase

Chlorosis induced by heavy metals has been generally

correlated with low plant Fe content, suggesting effects on

Fe mobilisation and uptake. Under Fe-deficient conditions,

dicotyledonous plants enhanced root Fe(III) reductase

activity, thus increasing the capacity to reduce Fe(III) to

Fe(II), the form in which roots absorb Fe (Alcantara et al.,

1994). Cr is reported to affect Fe uptake in dicots either by

inhibiting reduction of Fe(III) to Fe(II) or by competing with

Fe(II) at the site of absorption (Shanker, 2004). Chromium

application to iron-deficient Plantago lanceolata roots

increased the activity of root-associated Fe(III) reductase.

This effect was evident only with acceptors of the turbo

reductase and was not observed in iron-sufficient plants

(Wolfgang, 1996). In split-root experiments, which allowed

only a part of the root system to receive Cr while the other

portion was grown in iron-free medium, roots subjected to

either treatment showed an intermediate FeEDTA reductase

activity with respect to non-split control plants (Wolfgang,

1996). The addition of Cr(III) at 2 AM slightly inhibited

ferric chelate reductase in roots of plants grown under iron-

limited conditions; Cr(III) at 10 AM stimulated ferric chelate

reductase in roots from both iron-limited and iron-sufficient

media (Barton et al., 2000).

4.4.3. Plasma membrane H + ATPase

ATPase plays a significant role in the adaptation to

heavy-metal conditions and it is regulated at the

molecular and biochemical level (Dietz et al., 2001). A

toxic effect of Cr on the transport activities of plant cell

plasma membrane was suggested by Zaccheo et al.

(1982). After a short-term exposure to 2 AM Cr(VI), a

strong inhibition of both H+ and K+ uptake in maize root

segments was observed, while the transmembrane electric

potential was unchanged (Zaccheo et al., 1985). Pillay

(1994) found that ATPase activity increased at higher

treatment concentrations in a study on the effects of soil

Cr treatment on different metabolites and certain enzymes

of Helianthus suaveolens and Helianthus annus leaves.

The inhibition of ATPase activity could be due to

disruption of the membrane because of free radical

formation. The decrease in ATPase activity causes a

decrease in proton extrusion. This in turn could cause a

decrease in the transport activities of the root plasma

membrane, thus reducing the uptake of most nutrient

elements. It is also possible that Cr interfered with the

mechanism controlling the intracellular pH; this possibil-

ity is supported by the fact that Cr could be reduced in

the cells thereby utilizing the protons (Zaccheo et al.,

1985).

4.4.4. Antioxidant enzymes

Induction and activation of superoxide dismutase (SOD)

and of antioxidant catalase are some of the major metal

detoxification mechanisms in plants (Prasad, 1998;

Shanker et al., 2003a). Gwozdz et al. (1997) found that

at lower heavy metal concentrations, activity of antioxidant

enzymes increased, whereas at higher concentrations, the

SOD activity did not increase further and catalase activity

decreased. Pea plants exposed to environmentally relevant

(20 AM) and acute (200 AM) concentrations of Cr(VI) for

7 days affected total SOD activity of root mitochondria

differently. At 20 AM Cr(VI), SOD activity was found to

increase by 29%, whereas 200 AM Cr(VI) produced a

significant inhibition (Dixit et al., 2002). A decline in the

specific activity of catalase with increase in Cr concen-

tration from 20 to 80 ppm was observed (Jain et al., 2000).

Excess of Cr (0.5 mM) restricted the activity of catalase in

leaves of cauliflower (Chatterjee and Chatterjee, 2000).

H2O2 levels increased in both roots and leaves of sorghum

treated with either 50 AM Cr(VI) or 100 AM Cr(III) (Fig.

2a; Table 4). A similar increase in lipid peroxidation, in

terms of malondialdehyde formation, was observed with

these treatments (Fig. 2b).

In E. colona plants supplemented with Cr at 1.5 mg

L�1, activities of peroxidase and catalase were higher in

tolerant calluses than in non-tolerant ones (Samantaray et

al., 2001). Samantaray et al. (1999) used peroxidase and

catalase activities as enzyme markers for identifying Cr

tolerant mung bean cultivars. In wheat cultivar cv.

UP2003, the application of 0.05–0.5 mM Cr decreased

activities of both enzymes (Sharma and Sharma, 1996).

Sen et al. (1994) observed a decrease in catalase activity

and increase in peroxidase activity at concentrations

above 10 Ag L�1 Cr(VI), whereas the enzyme activities

Cr concentration

5

6

7

8

9

10

11

12

13

14

15

MD

A (

µmol

g-1D

W)

LeafRoot

C50µM

Cr concentration

0

5

10

15

H2O

2 (n

mol

g-1D

W)

Cr(III)Cr(III)100µM

Cr(VI)50µM

Cr(VI)100µM 50µM

Cr(III)Cr(III)100µM

Cr(VI)50µM

Cr(VI)100µM

C

a b**

**

* **

**

**

** **

**

****

**

Fig. 2. Levels of H2O2 (a) and lipid peroxidation expressed as malondialdehyde (MDA) (b) in roots and leaves of sorghum treated with indicated concentrations

of Cr(III) and Cr(VI). Data from Shanker and Pathmanabhan (2004).

A.K. Shanker et al. / Environment International 31 (2005) 739–753748

were least affected by Cr(VI) at lower concentrations.

The calli derived from L. leucocephala growing on

contaminated soil when supplemented with 15 AM Cr

exhibited higher catalase and peroxidase activities than

those from the uncontaminated soil. This provided

evidence that plant material from contaminated sources

were physiologically distinct from the uncontaminated

ones (Rout et al., 1999). The increase in antioxidant

enzymes activity observed might have been in direct

response to the generation of superoxide radical by Cr-

induced blockage of the electron transport chain in the

mitochondria. The higher increase noticed due to Cr(VI)

indicated that Cr(VI) addition probably generates more

singlet oxygen than Cr(III). The decrease in the activity

of the enzyme as the concentration of the external Cr

increased might be because of the inhibitory effect of Cr

ions on the enzyme system itself.

Root

C

Cr concentration

Cr(III)Cr(III)100µM50µM

Cr(VI)50µM

Cr(VI)100µM

500

1000

1500

2000

Tot

al G

luta

thio

ne (

nmol

g-1F

W)

*

*

**

*

**

a

Fig. 3. Levels of total glutathione (a) and GSH/GSSG ratio (b) in roots and leaves

from Shanker and Pathmanabhan (2004).

4.4.5. Glutathione

Stimulation of reduced glutathione (GSH) biosynthesis

was observed under stress conditions in poplar trees (Noctor

et al., 1998). Toppi et al. (2002) reported that GSH levels

ranged from about 30 nM SH g�1 fresh weight (FW) of root

extracts to 300 nM SH g�1 FW of leaf extracts in maize,

tomato and cauliflower plants following a Cr(VI) treatment

at concentrations of 5 and 10 mg L�1, these were higher

than control levels. Glutathione pool dynamics of sorghum

was affected, in terms of GSH and GSSG and the GSH/

GSSG ratio, by Cr speciation stress (Fig. 3; Table 4),

indicating that there is a possible role of this pathway in

countering Cr stress (Shanker and Pathmanabhan, 2004).

There was a marked decline in the GSH pool under Cr

speciation stress more severely in roots (Fig. 3). Several

authors have observed oxidation of different cellular thiols

such as GSH and cysteine by Cr(VI) in in vitro studies

Cr concentration

Leaf

C Cr(III)Cr(III)100µM50µM

Cr(VI)50µM

Cr(VI)100µM

GS

H/G

SS

H r

atio

1

2

3

4

5

**

****

**

**

b

of sorghum treated with indicated concentrations of Cr(III) and Cr(VI). Data

A.K. Shanker et al. / Environment International 31 (2005) 739–753 749

(McAuley and Olatunji, 1977a,b). Dichromate reacts with

GSH at the sulfhydryl group forming an unstable gluta-

thione–CrO3� complex (Brauer and Wetterhahn, 1991).

Thiolate complexes of Cr(VI) with g-glutamylcysteine, N-

acetylcysteine and cysteine have also been described

(Brauer et al., 1996). The interconversion of reduced and

oxidised forms of glutathione to maintain redox status of the

cell as well as to scavenge free radicals could have caused a

decrease in GSH. Metal-binding peptides like metallothio-

nein have been reported to have increased under Cr(VI)

stress (Shanker et al., 2004b).

5. Cr plant tolerance and phytoremediation

Literature survey shows that very few workers have

reported ameliorative measures for Cr toxicity in crop

plants. This is largely due the reason that most of the

research has been focused on enhancing phytoaccumulation

of Cr by plants and trees for its use in phytoremediation.

Impaired mineral nutrition due to Cr toxicity has been

corrected by the application of mycorrhizal inoculation.

Khan (2001) reported the potential of mycorrhizae in

protecting tree species Populus euroamericana, Acacia

arabica and Dalbergia sisso against the harmful effects of

heavy metal and phytoremediation of Cr contamination in

tannery effluent-polluted soils. Shanker et al. (in press) have

reported the possible use of Albizia amara as a potential Cr

phytoaccumulator. Karagiannidis and Hadjisavva Zinoviadi

(1998) studied the effect of the vesicular arbuscular

mycorrhizal fungus (VAMF) Glomus mosseae on growth,

yield and nutrient uptake of durum wheat and reported that

VAMF enhanced yield in wheat and simultaneously

decreased the Cr content in the plant. In a study on the

effects of Cr on the uptake and distribution of micronutrients

(Fe, Mn, Cu and Zn) in mycorrhizal soybean and maize in

sand culture, Davies et al. (2001) found that VAMF

enhanced the ability of sunflower plants to tolerate Cr;

similarly, Davies et al. (2002) reported that VAMF had a

positive effect on tissue mineral concentration, growth and

gas exchange in Cr-treated plants.

Glutathione and free amino acids are known to induce

heavy-metal tolerance by antioxidant action and metal-

chelating activity, respectively (Rauser, 1999). Increased S-

supply resulted in an overall increase in total S, sulfate and

GSH in leaves and tubers of potato. The concentrations of

the total free amino acid pools in leaves and tubers showed a

two- and threefold decrease, respectively, with increasing S-

supply (Hopkins et al., 2000). Hence, it is possible that

sulfate and iron supplementation can counter Cr toxicity in

crop plants.

The poor translocation of Cr from roots to shoots is a

major hurdle in using plants and trees for phytoremediation.

Pulford et al. (2001) in a study with temperate trees

confirmed that Cr was poorly taken up into the aerial

tissues but was held predominantly in the root. These

findings mean that the prospects for using trees as

phytoremediators on Cr-contaminated sites are low, their

main value being to stabilise and monitor a site (Shanker et

al., 2003b). This has lead to research with the prospects of

increasing Cr translocation by adding chemical and bio-

logical amendments to soil. It has been shown that if

chromate is reduced to chromic oxide by chemical or

biological methods, the inertness and insolubility of chromic

oxides in soil limited the formation of chromate and reduced

environmental risk (James, 1996). Mycorrhizae and organic

acids (citric and oxalic) have been reported to play an

important role in phytoremediation of Cr-contaminated soils

by enhancing Cr uptake and increasing translocation to

shoot (Chen et al., 1994; Davies et al., 2001).

Nutrient culture studies revealed a marked enhancement

in uptake and translocation of chelated 51Cr in P. vulgaris.

Cr chelated by DTPA was most effectively translocated

followed by 51Cr-EDTA and 51Cr-EDDHA (Athalye et al.,

1995). Significant increases in Cr accumulation from

Cr(III)-treated maize plants in the presence of increasing

concentrations of organic acid have been observed (Srivas-

tava et al., 1999a). Shahandeh and Hossner (2000b) have

reported a high increase in Cr uptake aided by organic acids.

Srivastava et al. (1999b) found that increasing concentra-

tions of organic acids resulted in increased uptake of Cr

without affecting the distribution in plant parts. Source-to-

plant transfer coefficients of Cr tended to increase with

increasing concentrations of organic acids in wheat. Chaney

et al. (1997) observed that phytostabilization [in situ

conversion of Cr(VI) in soil to Cr(III)] appears to have

strong promise with respect to chromium.

6. Concluding remarks

Having revised the overall picture of Cr toxicity in

plants, it is clear that the species of Cr are toxic at different

degrees at different stages of plant growth and develop-

ment and also that the toxicity is concentration and

medium dependent. The toxic properties of Cr(VI)

originate from the action of this form itself as an oxidizing

agent, as well as from the formation of free radicals during

the reduction of Cr(VI) to Cr(III) occurring inside the cell.

Cr(III), on the other hand, apart from generating reactive

oxygen species (ROS), if present in high concentrations,

can cause toxic effects due to its ability to coordinate

various organic compounds resulting in inhibition of some

metalloenzyme systems. The differential toxicity of these

two species can be explained by (i) translocation and

partitioning: Cr(VI) is actively taken up by a metabolic

driven process, whereas Cr(III) is probably passively taken

up and retained by cation exchange sites; in addition,

Cr(VI) competes with various elements of similar elec-

tronic structure; hence, it seems that Cr(VI) has an

advantage at the entry level into the plant system.

However, it should be noted that Cr(III) can easily enter

A.K. Shanker et al. / Environment International 31 (2005) 739–753750

the system if it is organically complexed at the rhizosphere

level. (ii) Damage due to ROS production: high concen-

trations of ROS at cellular level cause oxidative stress

which explains most of the visual Cr toxicity symptoms

observed at whole plant level. However, under appropriate

conditions, H2O2 can act as an oxidizing agent and may

oxidize Cr(III) to Cr(VI), an endogenous oxidation that

cannot be ruled out. On the other hand, Cr(III) can be

endogenously reduced to Cr(II) by biological reductants

such as cysteine and NADPH. In turn, the newly formed

Cr(II) reacts with H2O2 producing hydroxyl radicals and

causes tissue damage. Thus, one of the future challenges to

understand Cr toxicity would be to unravel the complete

picture of interconversion of the Cr species within the

plant system, after its uptake, on a time course at

environmentally relevant concentrations with emphasis at

different stages of plant development. (iii) Differential

defensive response: the high ROS production by Cr(VI)

could set in motion a chain of signaling response at gene

expression level which in turn could increase active

scavenging. Higher energy allocation for active scavenging

could deprive the plant of its quota of energy required for

normal growth; furthermore, the absence of heavy-metal

sequestering phytochelatins under Cr stress suggests that

this scavenging system is more energy intensive. In

contrast, a similar scenario under Cr(III) stress would not

be envisaged as the oxidizing potential of Cr(III) is less

and thus lesser amounts of ROS production and con-

sequently lesser toxicity may be assigned to this Cr

species.

References

Adriano DC. Trace Elements in the Terrestrial Environment. New York7

Springer Verlag; 1986. p. 105–23.

Alcantara E, Romera FJ, Canete M, De la Guardia MD. Effects of heavy

metals on both induction and function of root Fe(III) reductase in Fe-

deficient cucumber (Cucumis sativus L) plants. J Exp Bot 1994;45:

1983–98.

Anderson AJ, Meyer DR, Mayer FK. Heavy metal toxicities: levels of

nickel, cobalt and chromium in the soil and plants associated with visual

symptoms and variation in growth of an oat crop. Aust J Agric Res

1972;24:557–71.

Athalye VV, Ramachandran V, D’Souza TJ. Influence of chelating

agents on plant uptake of 51Cr, 210Pb and 210Po. Environ Pollut

1995;89:47–53.

Barcelo J, Poschenriender C, Ruano A, Gunse B. Leaf water potential in

Cr(VI) treated bean plants (Phaseolus vulgaris L). Plant Physiol Suppl

1985;77:163–4.

Barcelo J, Poschenrieder C, Gunse B. Water relations of chromium VI

treated bush bean plants (Phaseolus vulgaris L cv Contender) under

both normal and water stress conditions. J Exp Bot 1986;37:178–87.

Barcelo J, Poschenrieder C, Vazquez MD, Gunse B, Vernet JP. Beneficial

and toxic effects of chromium in plants: solution culture, pot and field

studies. Studies in Environmental Science No. 55, Paper Presented at

the 5th International Conference on Environmental Contamination,

Morges, Switzerland; 1993.

Barnhart J. Occurrences, uses, and properties of chromium. Regul Toxicol

Pharm 1997;26:S3–7.

Barton LL, Johnson GV, O’Nan AG, Wagener BM. Inhibition of ferric

chelate reductase in alfalfa roots by cobalt, nickel, chromium, and

copper. J Plant Nutr 2000;23:1833–45.

Bassi M, Corradi MG, Favali MA. Effect of chromium (VI) on two fresh

water plants, Lemna minor and Pistia stratiotes: II. Biochemical and

physiological observations. Cytobios 1990;62:101–9.

Becquer T, Quantin C, Sicot M, Boudot JP. Chromium availability in

ultramafic soils from New Caledonia. Sci Total Environ 2003;301:

251–61.

Behra TH, Panda SK, Patra HK. Chromium ion induced lipid peroxidation

in developing wheat seedlings: role of growth hormones. India J Plant

Physiol 1999;4:236–8.

Bera AK, Kanta-Bokaria AK, Bokaria K. Effect of tannery effluent on seed

germination, seedling growth and chloroplast pigment content in

mungbean (Vigna radiata LWilczek). Environ Ecol 1999;17(4):958–61.

Biacs PA, Daood HG, Kadar I. Effect of Mo, Se, Zn, and Cr treatments on

the yield, element concentration, and carotenoid content of carrot. J

Agric Food Chem 1995;43:589–91.

Biddappa CC, Bopaiah MG. Effect of heavy metals on the distribution of P,

K, Ca, Mg and micronutrients in the cellular constituents of coconut

leaf. J Plantation Crops 1989;17:1–9.

Bishnoi NR, Chugh LK, Sawhney SK. Effect of chromium on photosyn-

thesis, respiration and nitrogen fixation in pea (Pisum sativum L)

seedlings. J Plant Physiol 1993a;142:25–30.

Bishnoi NR, Dua A, Gupta VK, Sawhney SK. Effect of chromium on seed

germination, seedling growth and yield of peas. Agric Ecosyst Environ

1993b;47:47–57.

Bonet A, Poschenrieder C, Barcelo J. Chromium III–iron interaction in Fe-

deficient and Fe-sufficient bean plants: I. Growth and nutrient content. J

Plant Nutr 1991;14:403–14.

Boonyapookana B, Upatham ES, Kruatrachue M, Pokethitiyook P,

Singhakaew S. Phytoaccumulation and phytotoxicity of cadmium

and chromium in duckweed Wolffia globosa. Int J Phytoremed

2002;4:87–100.

Brauer SL, Wetterhahn KE. Chromium (VI) forms thiolate complex with

glutathione. J Am Chem Soc 1991;113:3001–7.

Brauer SL, Hneihen AS, McBride JS, Wetterhahn KE. Chromium (VI)

forms thiolate complexes with glutamylcysteine, N-acetylcysteine, and

methyl ester of N-acetylcysteine. Inorg Chem 1996;35:373–81.

Breckle SW. Growth under stress: heavy metals. In: Waisel Y, Eshel A,

Kafkafi U, editors. Plant Root: The Hidden Half. NY, USA7 Marcel

Dekker; 1991. p. 351–73.

Cary EE, Allaway WH, Olsen OE. Control of chromium concentrations in

food plants: 2 Chemistry of chromium in soils and its availability to

plants. J Agric Food Chem 1977a;25:305–9.

Cary EE, Allaway WH, Olsen OE. Control of chromium concentration in

food plants: I Absorption and translocation of chromium by plants. J

Agric Food Chem 1977b;25:300–4.

Cervantes C, Garcia JC, Devars S, Corona FG, Tavera HL, Torres-guzman J

Carlos, et al. Interactions of chromium with micro-organisms and

plants. FEMS Microbiol Rev 2001;25:335–47.

Chandra P, Sinha S, Rai UN. Bioremediation of Cr from water and soil by

vascular aquatic plants. In: Kruger EL, Anderson TA, Coats JR, editors.

Phytoremediation of Soil and Water Contaminants. ACS Symposium

Series, vol. 664. Washington, DC7 American Chemical Society; 1997.

p. 274–82.

Chaney RL, Malik M, Li YM, Brown SL, Angle JS, Baker AJM.

Phytoremediation of soil metals. Curr Opin Biotechnol 1997;8:279–84.

Chatterjee J, Chatterjee C. Phytotoxicity of cobalt, chromium and copper in

cauliflower. Environ Pollut 2000;109:69–74.

Chen YX, Zhu ZX, He ZY. Pollution behaviour of organic Cr(III)

complexes in soil–plant system. Chin J Appl Ecol 1994;5:187–91.

Chen NC, Kanazawa S, Horiguchi T, Chen NC. Effect of chromium on

some enzyme activities in the wheat rhizosphere. Soil Microorg

2001;55:3–10.

Clijsters H, Van Assche F. Inhibition of photosynthesis by heavy metals.

Photosynth Res 1985;7:31–40.

A.K. Shanker et al. / Environment International 31 (2005) 739–753 751

Corradi MG, Bianchi A, Albasini A. Chromium toxicity in Salivia sclarea:

I Effects of hexavalent chromium on seed germination and seedling

development. Environ Exp Bot 1993;33:405–13.

Davies FT, Puryear JD, Newton RJ, Egilla JN, Grossi JAS. Mycorrhizal

fungi enhance accumulation and tolerance of chromium in sunflower

(Helianthus annuus). J Plant Physiol 2001;158:777–86.

Davies FT, Puryear JD, Newton RJ, Egilla JN, Grossi JAS. Mycorrhizal

fungi increase chromium uptake by sunflower plants: influence on

tissue mineral concentration, growth, and gas exchange. J Plant Nutr

2002;25:2389–407.

Desmet GA, de Ruyter GA, Rigoet A. Absorption and metabolism of

Cr(VI) by isolated chloroplasts. Phytochemisty 1975;14:2585–8.

Dietz KJ, Tavakoli N, Kluge C, Mimura T, Sharma SS, Harris GC, et al.

Significance of the V-type ATPase for the adaptation to stressful growth

conditions and its regulation on the molecular and biochemical level. J

Exp Bot 2001;52:1969–80.

Dixit V, Pandey V, Shyam R. Chromium ions inactivate electron transport

and enhance superoxide generation in vivo in pea (Pisum sativum L.cv.

Azad) root mitochondria. Plant Cell Environ 2002;25:687–90.

Foy CD, Chaney RL, White MC. The physiology of metal toxicity in

plants. Ann Rev Plant Physiol 1978;29:511–66.

Goldbold DL, Kettner C. Use of root elongation studies to determine

aluminium and lead toxicity in Piea abies seedlings. J Plant Physiol

1991;138:231–5.

Golovatyj SE, Bogatyreva EN, Golovatyi SE. Effect of levels of chromium

content in a soil on its distribution in organs of corn plants. Soil Res

Fert 1999;197–204.

Grubinger VP, Gutenmann WH, Doss GJ, Rutzke M, Lisk DJ. Chromium in

Swiss chard grown on soil amended with tannery meal fertilizer.

Chemosphere 1994;28:717–20.

Gupta K, Mehta R, Kumar N, Dahiya DS. Effect of chromium (VI) on

phosphorus fractions in developing sunflower seeds (Helianthus

annuus L). Crop Res 2000;20:46–51.

Gwozdz EA, Przymusinski R, Rucinska R, Deckert J. Plant cell responses

to heavy metals: molecular and physiological aspects. Acta Physiol

Plant 1997;19:459–65.

Hanus J, Tomas J. An investigation of chromium content and its uptake

from soil in white mustard. Acta Fytotech 1993;48:39–47.

Hara T, Sonoda Y. Comparison of the toxicity of heavy metals to cabbage

growth. Plant Soil 1979;51:127–33.

Hopkins L, Malcolm J, Hawkesford J. S-supply, free sulphur and free

amino acid pools in potato (Solanum tuberosum l. Cv Desiree). In:

Brunold C, editor. Sulphur Nutrition and Sulfur Assimilation in Higher

Plants; 2000, p. 259–61.

Huffman Jr EWD, Allaway HW. Chromium in plants: distribution in

tissues, organelles, and extracts and availability of bean leaf Cr to

animals. J Agric Food Chem 1973a;21:982–6.

Huffman Jr EWD, Allaway WH. Growth of plants in solution culture

containing low levels of chromium. Plant Physiol 1973b;52:72–5.

Iqbal MZ, Saeeda S, Shafiq Muhammad. Effects of chromium on an

important arid tree (Caesalpinia pulcherrima) of Karachi city, Pakistan.

Ekol Bratislava 2001;20:414–22.

Jain R, Srivastava S, Madan VK, Jain R. Influence of chromium on growth

and cell division of sugarcane. Indian J Plant Physiol 2000;5:228–31.

James BR. The challenge of remediating chromium-contaminated soils.

Environ Sci Technol 1996;30:248A–51A.

Jetly V, Srivastava AK. Monitoring of chromium phytotoxicity in some

crops: effect on seed germination and seedling growth. Soc Adv Bot

1995;23:273–9.

Jin-Hong Q, Zayed QA, YongLiang Zhu, Mei Yu, Terry N, Qian JH, et al.

Phytoaccumulation of trace elements by wetland plants: III. Uptake and

accumulation of ten trace elements by twelve plant species. J Environ

Qual 1999;28:1448–55.

Joseph GW, Merrilee RA, Raymond E. Comparative toxicities of six heavy

metals using root elongation and shoot growth in three plant species.

The symposium on environmental toxicology and risk assessment,

Atlanta, GA, USA; 1995. p. 26–9.

Karagiannidis N, Hadjisavva Zinoviadi S. The mycorrhizal fungus Glomus

mosseae enhances growth, yield and chemical composition of a durum

wheat variety in 10 different soils. Nutr Cycl Agroecosyst 1998;52:1–7.

Karunyal S, Renuga G, Paliwal K. Effects of tannery effluent on seed

germination, leaf area, biomass and mineral content of some plants.

Bioresour Technol 1994;47:215–8.

Khan AG. Relationships between chromium bio magnification ratio,

accumulation factor, and mycorrhizae in plants growing on tannery

effluent-polluted soil. Environ Int 2001;26:417–23.

Khan AG, Kuek C, Chaudhry TM, Khoo CS, Hayes WJ. Role of plants,

mycorrhizae and phytochelators in heavy metal contaminated land

remediation. Chemosphere 2000;41:197–207.

Khan S, Ullah SM, Sarwar KS. Interaction of chromium and copper with

nutrient elements in rice (Oryza sativa cv BR-11). Bull Inst Trop Agric,

Kyushu Univ 2001;23:35–9.

Kimbrough DE, Cohen Y, Winer AM, Creelman L, Mabuni C. A critical

assessment of chromium in the environment. Crit Rev Environ Sci

Technol 1999;29:1–46.

Kocik K, Ilavsky J. Effect of Sr and Cr on the quantity and quality of the

biomass of field crops. Production and utilization of agricultural and

forest biomass for energy: Proceedings of a seminar held at Zvolen,

Slovakia, p. 168–78.

Kotas J, Stasicka Z. Commentary: chromium occurrence in the environment

and methods of its speciation. Environ Pollut 2000;107:263–83.

Krupa Z, Baszynski T. Some aspects of heavy metals toxicity towards

photosynthetic apparatus—direct and indirect effects on light and dark

reactions. Acta Physiol Plant 1995;17:177–90.

McAuley A, Olatunji MA. Metal ion oxidations in solution. Part XVIII.

Characterization rates, and mechanisms of formation of the intermedi-

ates in the oxidation of thiols by chromium (VI). Can J Chem

1977a;55:3328–34.

McAuley A, Olatunji MA. Metal ion oxidations in solution. Part XIX.

Redox pathways in the oxidation of penicillamine and glutathione by

chromium (VI). Can J Chem 1977b;55:3335–40.

McGrath SP. The uptake and translocation of tri- and hexavalent chromium

and effects on the growth of oat in flowing nutrient solution and in soil.

New Phytol 1982;92:381–90.

Mei B, Puryear JD, Newton RJ. Assessment of Cr tolerance and

accumulation in selected plant species. Plant Soil 2002;247:223–31.

Mishra S, Shanker K, Srivastava MM, Srivastava S, Shrivastav R, Dass S,

et al. A study on the uptake of trivalent and hexavalent chromium by

paddy (Oryza sativa): possible chemical modifications in rhizosphere.

Agric Ecosyst Environ 1997;62:53–8.

Moral R, Navarro Pedreno J, Gomez I, Mataix J. Effects of chromium on

the nutrient element content and morphology of tomato. J Plant Nutr

1995;18:815–22.

Moral R, Gomez I, Pedreno JN, Mataix J. Absorption of Cr and effects on

micronutrient content in tomato plant (Lycopersicum esculentum M).

Agrochimica 1996;40:132–8.

Nichols PB, Couch JD, Al Hamdani SH. Selected physiological responses

of Salvinia minima to different chromium concentrations. Aquat Bot

2000;68:313–9.

Noctor G, Arisi ACM, Jouanin L, Foyer CH. Manipulation of glutathione

and amino acids biosynthesis in the chloroplast. Plant Physiol

1998;118:471–82.

Nriagu JO. Production and uses of chromium. Chromium in natural and

human environment. New York, USA7 John Wiley and Sons; 1988.

p. 81–105.

Ottabbong E. Chemistry of Cr in some Swedish soil III. Assessment of Cr

toxicity and Cr�P interactions in rye grass (Lolium perenne). Acta

Agric Scand 1989a;39:139–47.

Ottabbong E. Chemistry of Cr in some Swedish soil: II. Fate and impact of

added Cr on pH and stutus of soluble Mn in four soils. Acta Agric

Scand 1989b;39:131–8.

Ottabbong E. Chemistry of Cr in some Swedish soil: IV. Influence of CrO2

and KHPO4 on uptake and translocation of Mn, Cu, Zn, Fe and Al by

rye grass (Lolium perenne). Acta Agric Scand 1989c;39:149–57.

A.K. Shanker et al. / Environment International 31 (2005) 739–753752

Panda SK, Patra HK. Nitrate and ammonium ions effect on the chromium

toxicity in developing wheat seedlings. P Natl Acad Sci India B

2000;70:75–80.

Parr PD, Taylor Jr FG. Germination and growth effects of hexavalent

chromium in Orocol TL (a corrosion inhibitor) on Phaseolus vulgaris.

Environ Int 1982;7:197–202.

Pedreno NJI, Gomez R, Moral G, Palacios J, Mataix J. Heavy metals and

plant nutrition and development. Recent Res Dev Phytochem 1997;1:

173–9.

Peralta JR, Gardea Torresdey JL, Tiemann KJ, Gomez E, Arteaga S, Rascon

E, et al. Uptake and effects of five heavy metals on seed germination

and plant growth in alfalfa (Medicago sativa) L. B Environ Contam

Toxicol 2001;66(6):727–34.

Pillay SV. Biochemical changes in Hyptis suaveolens (L) Poit and

Helianthus annuus L in response to chromium treatment. J Phytol

Res 1994;7:165–7.

Poschenrieder C, Gunse B, Barcelo J. Chromium-induced inhibition of

ethylene evolution in bean (Phaseolus vulgaris) leaves. Physiol Plant

1993;89:404–8.

Prasad MNV. Metal-biomolecule complexes in plants: occurrence, func-

tions, and applications. Analusis 1998;26;28.

Prasad MNV, Greger M, Landberg T. Acacia nilotica L bark removes

toxic elements from solution: corroboration from toxicity bioassay

using Salix viminalis L in hydroponic system. Int J Phytoremed

2001;3:289–300.

Pulford ID, Watson C, McGregor SD. Uptake of chromium by trees:

prospects for phytoremediation. Environ Geochem Health 2001;23:

307–11.

Ramachandran V, D’Souza TJ, Mistry KB. Uptake and transport of

chromium in plants. J Nucl Agric Biol 1980;9:126–9.

Rauser WE. The structure and function of metal chelators produced by

plants. Cell Biol Biophys 1999;31:19–48.

Rout GR, Samantaray S, Das P. Differential chromium tolerance among

eight mungbean cultivars grown in nutrient culture. J Plant Nutr

1997;20:473–83.

Rout GR, Samantaray S, Das P. Chromium, nickel and zinc tolerance in

Leucaena leucocephala (K8). Silvae Genet 1999;48:151–7.

Rout GR, Sanghamitra S, Das P. Effects of chromium and nickel on

germination and growth in tolerant and non-tolerant populations of

Echinochloa colona (L). Chemosphere 2000;40:855–9.

Saltabas O, Akcin G. Removal of chromium, copper and nickel by

water hyacinth (Eichhornia crassipes). Toxicol Environ Chem 1994;

41:131–4.

Samantaray S. Biochemical responses of Cr-tolerant and Cr-sensitive mung

bean cultivars grown on varying levels of chromium. Chemosphere

2002;47:1065–72.

Samantaray S, Rout GR, Das P. Studies on differential tolerance of

mungbean cultivars to metalliferous minewastes. Agribiol Res

1999;52:193–201.

Samantaray S, Rout GR, Das P. Induction, selection and characterization of

Cr and Ni-tolerant cell lines of Echinochloa colona (L) in vitro. J Plant

Physiol 2001;158:1281–90.

Schmfger, MEV. Phytochelatins: Complexation of Metals and Metalloids,

Studies on the Phytochelatin Synthase. PhD Thesis, Munich University

of Technology (TUM), Munich, Germany; 2001.

Sen AK, Mondal NG, Mandal S. Toxic effects of chromium (VI) on the

plant Salvinia natans L. Environ Ecol 1994;12:279–83.

Shahandeh H, Hossner LR. Enhancement of Cr(III) phytoaccumulation.

Int J Phytoremed 2000a;2:269–86.

Shahandeh H, Hossner LR. Plant screening for chromium phytoremedia-

tion. Int J Phytoremed 2000b;2:31–51.

Shanker AK. Physiological, biochemical and molecular aspects of chro-

mium toxicity and tolerance in selected crops and tree species. PhD

Thesis, Tamil Nadu Agricultural University, Coimbatore, India; 2003.

Shanker, AK. Plasma Membrane H+ ATPase and Fe(III) Reductase: Key

Enzymes When Engineering Tolerance to Chromium Speciation Stress

in Plants. Paper in BIOHORIZON 2004 6th National Symposium on

Biochemical engineering and biotechnogy Held at Indian Institute of

Technology, New Delhi 12th–13th March 2004.

Shanker AK, Pathmanabhan G. Speciation dependant antioxidative

response in roots and leaves of Sorghum (Sorghum bicolor (L) Moench

cv CO 27) under Cr(III) and Cr(VI) stress. Plant Soil 2004;265:141–51.

Shanker AK, Sudhagar R, Pathmanabhan G. Growth, Phytochelatin SH and

antioxidative response of Sunflower as affected by chromium speci-

ation. 2nd International Congress of Plant Physiology on sustainable

plant productivity under changing environment, New Delhi, India,

2003a.

Shanker AK, Djanaguiraman M, Pathmanabhan G, Sudhagar R, Avudai-

nayagam S. Uptake and phytoaccumulation of chromium by selected

tree species. Proceedings of the International Conference on Water and

Environment held in Bhopal, M.P. India, 2003b.

Shanker AK, Djanaguiraman M, Sudhagar R, Chandrashekar CN,

Pathmanabhan G. Differential antioxidative response of ascorbate

glutathione pathway enzymes and metabolites to chromium speciation

stress in green gram (Vigna radiata (L) R Wilczek, cv CO 4) roots.

Plant Sci 2004a;166:1035–43.

Shanker AK, Djanaguiraman M, Sudhagar R, Jayaram R, Pathmanabhan

G. Expression of metallothionein 3 (MT3) like protein mRNA in

Sorghum cultivars under chromium (VI) stress. Curr Sci

2004b;86(7):901–2.

Shanker AK, Ravichandran V, Pathmanabhan G. Phytoaccumulation of

chromium by some multi purpose tree seedlings. Agroforestry Systems;

in press.

Sharma DC, Mehrotra SC. Chromium toxicity effects on wheat

(Triticum aestivum L cv HD 2204). Indian J Environ Health 1993;

35:330–2.

Sharma DC, Pant RC. Chromium uptake and its effects on certain plant

nutrients in maize (Zea mays L. cv. Ganga 5). J Environ Sci Health A

1994;29:941–8.

Sharma DC, Sharma CP. Chromium uptake and its effects on growth and

biological yield of wheat. Cereal Res Commun 1993;21:317–21.

Sharma DC, Sharma CP. Chromium uptake and toxicity effects on growth

and metabolic activities in wheat, Triticum aestivum L. cv. UP 2003.

Indian J Exp Biol 1996;34:689–91.

Shewry PR, Peterson JP. The uptake of chromium by barley seedlings

(Hordeum vulgare L). J Exp Bot 1974;25:785–97.

Singaram P. Removal of chromium from tannery effluent by using water

weeds. Indian J Environ Health 1994;36:197–9.

Singh AK. Effect of trivalent and hexavalent chromium on spinach

(Spinacea oleracea L). Environ Ecol 2001;19:807–10.

Skeffington RA, Shewry PR, Petersen PJ. Chromium uptake and transport

in barley seedlings Hordeum vulgare. Planta 1976;132:209–14.

Srivastava MM, Juneja A, Dass S, Srivastava R, Srivastava S, Mishra S,

et al. Studies on the uptake of trivalent and hexavalent chromium by

onion (Allium cepa). Chem Speciat Bioavailab 1994;6:27–30.

Srivastava S, Nigam R, Prakash S, Srivastava MM. Mobilization of

trivalent chromium in presence of organic acids: a hydroponic study of

wheat plant (Triticum vulgare). B Environ Contam Toxicol 1999a;63:

524–30.

Srivastava S, Prakash S, Srivastava MM. Chromium mobilization and plant

availability—the impact of organic complexing ligands. Plant Soil

1999b;212:203–8.

Sujatha P, Gupta A. Tannery effluent characteristics and its effects on

agriculture. J Ecotoxicol Environ Monit 1996;6:45–8.

Suseela MR, Sinha S, Singh S, Saxena R. Accumulation of chromium and

scanning electron microscopic studies in scirpus lacustris l treated with

metal and tannery effluent. Bull Environ Contam Toxicol 2002;68:

540–8.

Tang SR, Wilke BM, Brooks RR, Tang SR. Heavy-metal uptake by metal-

tolerant Elsholtzia haichowensis and Commelina communis from

China. Commun Soil Sci Plant Anal 2001;32(5–6):895–905.

Toppi LSD, Fossati F, Musetti R, Mikerezi I, Favali MA. Effects of

hexavalent chromium on maize, tomato, and cauliflower plants. J Plant

Nutr 2002;25:701–17.

A.K. Shanker et al. / Environment International 31 (2005) 739–753 753

Tripathi AK, Tripathi Sadhna, Tripathi S. Changes in some physiological

and biochemical characters in Albizia lebbek as bio-indicators of heavy

metal toxicity. J Environ Biol 1999;20:93–8.

Turner MA, Rust RH. Effects of chromium on growth and mineral nutrition

of soybeans. Soil Sci Soc Am Proc 1971;35:755–8.

Vajpayee P, Rai, UN, Sinha S, Tripathi RD, Chandra P. Bioremediation of

tannery effluent by aquatic macrophytes. Bull Environ Cont Toxicol

1995;55:546–53 [23].

Vajpayee P, Sharma SC, Tripathi RD, Rai UN, Yunus M. Bioaccumulation

of chromium and toxicity to photosynthetic pigments, nitrate reductase

activity and protein content of Nelumbo nucifera Gaertn. Chemosphere

1999;39:2159–69.

Vajpayee P, Tripathi RD, Rai UN, Ali MB, Singh SN. Chromium (VI)

accumulation reduces chlorophyll biosynthesis, nitrate reductase

activity and protein content in Nymphaea alba L. Chemosphere

2000;41:1075–82.

Vajpayee P, Rai UN, Ali MB, Tripathi RD, Yadav V, Sinha S, et al.

Chromium induced physiological changes in Vallisneria spiralis L and

its role in phytoremediation of tannery effluent. Bull Environ Contam

Toxicol 2001;67(2):246–56.

Van Assche F, Clijsters H. Multiple effects of heavy metals on photosyn-

thesis. In: Marcelle R, editor. Effects of stress on photosynthesis. The

Hague7 Nijhoff/Junk; 1983. p. 371–82.

Vazques MD, Poschenrieder Ch, Barcelo J. Chromium (VI) in-

duced structural changes in bush bean plants. Ann Bot 1987;59:

427–38.

Wahaab RA, Lubberding HJ, Alaerts GJ, El Gohary F. Copper and chro-

mium (III) uptake by duckweed. Water Sci Technol 1995;32:105–10.

Wallace A, Soufi SM, Cha JW, Romney EM. Some effects of chro-

mium toxicity on bush bean plants grown in soil. Plant Soil 1976;44:

471–3.

Wolfgang S. Influence of chromium(III) on root-associated Fe(III)

reductase in Plantago lanceolata L. J Exp Bot 1996;47:805–10.

Zaccheo P, Genevini PL, Cocucci S. Chromium ions toxicity on the

membrane transport mechanism in segments of maize seedling roots.

J Plant Nutr 1982;5:1217–27.

Zaccheo P, Cocucci M, Cocucci S. Effects of Cr on proton extrusion,

potassium uptake and transmembrane electric potential in maize root

segments. Plant Cell Environ 1985;8:721–6.

Zayed A, Terry N. Chromium in the environment: factors affecting

biological remediation. Plant Soil 2003;249:139–56.

Zayed A, Lytle CM, Jin-Hong Q, Terry N, Qian JH. Chromium

accumulation, translocation and chemical speciation in vegetable crops.

Planta 1998;206:293–9.

Zeid IM. Responses of Phaseolus vulgaris to chromium and cobalt

treatments. Biol Plant 2001;44:111–5.

Zlatareva E., Nikolov N., Nikolaev A.. Uptake of Cr(III) by alfalfa

depending on pH and the level of pollution of the soil. Pochvoznanie

Agrokhimiya Ekologiya 1999;34:49–53.

Zurayk R, Sukkariyah B, Baalbaki R. Common hydrophytes as bioindica-

tors of nickel, chromium and cadmium pollution. Water Air Soil Pollut

2001;127:373–88.